Unless I'm not reading correctly the whole Performance Level/Read Delay as written is ass-backwards. The lower numerically the Performance Level is set the higher the performance. Setting the Read Delay to enabled give a -1. Such that if the Performance Level was set at 7 and all Read Delays were set to Enabled, from a practical standpoint, the board would be running at a performance Level of 6 (higher performance).

GTL adjustment is more then a means of stability. Pinned to their optimal setpoint the overclock will require less VCORE, VTT, NB and memory voltage. For the brute-force approach a person is best off to ignore GTL tuning and concentrate on voltages.